A cryptography method that uses quantum mechanics includes Yuen quantum cryptography. The protocol for Yuen quantum cryptography is called Y-00. It conceals an optical signal that has been subjected to intensity modulation or phase modulation by using the quantum fluctuation (noise) of laser light to diffuse the signal. Quantum cryptography is cryptography in which a physical phenomenon is used. Quantum cryptography takes a less time in encryption and decryption and is superior in resistance to eavesdropping when compared with mathematical cryptography.
A related technology is disclosed in Japanese Laid-open Patent Publication No. 2011-61292 or Japanese Laid-open Patent Publication No. 2012-74980.